HyukjinKwon commented on a change in pull request #27517:
[WIP][SPARK-29721][SQL] Prune unnecessary nested fields from Generate without
Project
URL: https://github.com/apache/spark/pull/27517#discussion_r376898122
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
##########
@@ -155,6 +161,56 @@ object NestedColumnAliasing {
case MapType(keyType, valueType, _) => totalFieldNum(keyType) +
totalFieldNum(valueType)
case _ => 1 // UDT and others
}
+}
+
+/**
+ * This prunes unnessary nested columns from `Generate` and optional `Project`
on top
+ * of it.
+ */
+object GeneratorNestedColumnAliasing {
+ def unapply(plan: LogicalPlan): Option[LogicalPlan] = plan match {
+ // Either `nestedPruningOnExpressions` or `nestedSchemaPruningEnabled` is
enabled, we
+ // need to prune nested columns through Project and under Generate. The
difference is
+ // when `nestedSchemaPruningEnabled` is on, nested columns will be pruned
further at
+ // file format readers if it is supported.
+ case Project(projectList, g: Generate) if
(SQLConf.get.nestedPruningOnExpressions ||
+ SQLConf.get.nestedSchemaPruningEnabled) &&
canPruneGenerator(g.generator) =>
+ // On top on `Generate`, a `Project` that might have nested column
accessors.
+ // We try to get alias maps for both project list and generator's
children expressions.
+ NestedColumnAliasing.getAliasSubMap(projectList ++
g.generator.children).map {
+ case (nestedFieldToAlias, attrToAliases) =>
+ val newChild = pruneGenerate(g, nestedFieldToAlias, attrToAliases)
+ Project(NestedColumnAliasing.getNewProjectList(projectList,
nestedFieldToAlias), newChild)
+ }
+
+ case g: Generate if SQLConf.get.nestedSchemaPruningEnabled &&
+ canPruneGenerator(g.generator) =>
+ // For the child outputs required by the operator on top of `Generate`,
we do not want
+ // to prune it.
Review comment:
@viirya I think it's better to elaborate this comment a bit more the reason
why we don't want to prune it. It's basically to keep the child in case it's
referred from higher projection (that was missed from `case
Project(projectList, g: Generate)` case).
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